1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly, to an image processing apparatus comprising means for judging whether each pixel of image data is included in a first area of pseudo half-tone image or a second area of non-half-tone image.
2. Description of Related Art
In a conventional facsimile apparatus, in order to transmit an image signal through a public telephone line, a transmitter converts image data of non-half-tone images such as characters into binary image data of non-half-tone image by binarizing them using a predetermined threshold value and then transmits the converted binary image data to a receiver of the other party. The transmitter converts multi-value image data of half-tone-images into binary image data of pseudo half-tone image by binarizing them using a dither method and then transmits the converted binary image data to the receiver of the other party. It is to be noted that multi-value image data means image data of multi-gradation stages in the specification. On the other hand, the receiver of the other party performs different processes depending on the kind of the image of the received image data such as non-half-tone image, pseudo half-tone image or the like. Namely, it is necessary for the receiver to perform the following processes:
(a) a process for extracting each kind of binary image data; PA1 (b) a process for switching over the method for converting the pixel density thereof; and PA1 (c) a process for switching over the decoding method such as the method for compressing image data or the like. PA1 (a) setting a mask for surrounding a plurality of pixels including a specified pixel; PA1 (b) taking out a pixel pattern formed based on values of a plurality of pixels within the mask; PA1 (c) generating an image-area signal corresponding to the above-mentioned pixel pattern according to a table of image area signals on the pixel patterns previously stored in a storage-unit dividing all the pixel patterns which may be caused into the dot photograph area and the document area; and PA1 (d) outputting the generated image area signal as the image area signal corresponding to the specified pixel. Concretely, the respective pixel patterns are previously stored in a table ROM by dividing the pixel pattern into the dot photograph area and the document area, and when an image signal to be processed is inputted to an address terminal of the table ROM, resulting in the image area signal in the data terminal of the table ROM. PA1 (a) recovering a half-tone image from the inputted binary image data; and PA1 (b) performing predetermined processes such as a magnification and reduction process, an image emphasis process or the like for the recovered half-tone image. In the third conventional method, in order to recover multi-value image data from binary image data, a window in a square shape having a predetermined size is provided close to a specified pixel to be recovered, and then, a smoothing process is performed for the inputted image data within the provided window. PA1 (a) dividing means for dividing binarized image information into predetermined blocks; PA1 (b) judging means for judging the image tone by each block; and PA1 (c) converting means for converting the binarized image information within the block into multi-value image data according to the judgment result thereof. In the fourth conventional apparatus, upon transmitting image data and storing them, there are used binary image data so as to display and edit them more efficiently. Further, upon reproducing the image, there is used a multi-value representation close to an analogue image. Concretely, the judgment means is constituted by an image judgment table ROM for judging the image tone using a pattern matching method within each block corresponding to a size of a dither matrix, and the converting means is constituted by a conversion ROM. PA1 (1) After dividing binary image data into respective blocks, a number of black pixels within each block is counted, a density level of each block is presumed based on the number of black pixels, and then, multi-value image data are recovered based on the presumed density level thereof. PA1 (2) After dividing binary image data into respective unit areas, a number of black pixels within each unit area is counted, and there is obtained the dispersion of the number of black pixels within a predetermined block area composed of not only a specified unit area but also a predetermined number of unit areas adjacent to the specified unit area. Then, when the dispersion thereof is relatively small, an arrangement of black pixels is obtained using a density matrix pattern having a relatively larger size, and then, multi-value image data are recovered based on the arrangement of black pixels. On the other hand, when the dispersion thereof is relatively large, an arrangement of black pixels is obtained using a density matrix pattern having a relatively small size, and then, multi-value image data are recovered based on the arrangement of black pixels. PA1 (3) There is prepared a scanning opening having a size of N.times.N pixels for binary image data, a number of black pixels within each scanning opening is counted shifting the scanning opening by one pixel. Thereafter, the counted number of black pixels is set as a density level, sequentially, and then, multi-value image data are recovered based on the set density level. This method corresponds to a convolution process for binary image data using a spatial filter comprising all the pixels of one or black within a 4.times.4 window.
Therefore, it is necessary to automatically judge whether or not the received image data are binary image data of non-half-tone image or binary image data of pseudo half-tone image. There is disclosed in the Japanese Patent examined publication No. 63-11832, a method for judging the kind of the received image data and generating an image area signal having the judgment result (referred to as a first conventional method hereinafter). The first conventional method is provided for judging whether or not respective pixels of an image signal having both a dot photograph area and a document area of characters are included in the dot photograph area or the document area, and for generating an image area signal for representing the judged image area. Namely, the first conventional method includes the following steps:
Further, there is suggested in Yoshinobu MITA et al, "Higher fine multi-value recovery of binary image by Neural Network", Japan Hard copy, '90, NIP-24 pp 233-236, 1990, an apparatus for automatically judging whether or not inputted binary image data are binary image data of non-half-tone image or binary image data of-pseudo half-tone image (referred to as a second conventional apparatus hereinafter). In the second conventional apparatus, by using a back propagation method for Neural Network, there is performed not only a process for converting inputted binary image data into multi-value image data using a Neural Network but also a process for dividing inputted binary image data into predetermined kinds of image area and for converting them into multi-value image data depending on the divided image area using the Neural Network. The Neural Network of the second conventional apparatus has a three-layer structure comprising an input layer, an intermediate layer and an output layer. In the input layer, there are provided a number of units corresponding to a number of pixels included in a window provided close to a specified pixel, and there is provided in the output layer one unit for outputting multi-value image data.
However, in the first conventional method, since there is provided the pixel pattern table ROM for judging image areas, as the area to be judged for area judgment increases, the manufacturing cost thereof increases. Further, in the second conventional apparatus, the composition of the apparatus is complicated, and the processing speed is extremely low.
Further, when an image including a broken line is binarized, the binarized image becomes similar to a half-tone image. Therefore, there is a possibility of erroneously judging the image areas in the conventional method and apparatus.
Furthermore, in a conventional facsimile apparatus, in order to transmit an image signal through a public telephone line, a transmitter converts a half-tone image such as a photograph image or the like into binary image data of pseudo half-tone image by binarizing them using a dither method or the like, and then, transmits the converted image data to a receiver of the other party. On the other hand, the receiver recovers multi-value image data from the received binary image data of pseudo half-tone.
Further, recently, there has been put into practice a color laser printer for recording an image of multi-value image data at a high speed and with a high resolution, however, there have been widely used binary printers for recording binary image data, generally. In order to store multi-value image data in a storage unit, it is necessary to provide the storage unit having a relatively large capacity.
In order to solve the above problem, the following method is suggested. Namely, the multi-value image data are converted into binary image data, and then, the converted binary image data are stored in the storage unit. Furthermore, upon processing the binary image data or recording the binary image data, after reading out the above binary image data from the storage unit, multi-value image data are recovered from the read binary image data.
The method and apparatus of this type are disclosed in the Japanese patent laid-open publications Nos. 62-114378 and 62-107573.
The image processing method disclosed in the former publication (referred to as a third conventional method hereinafter) includes the following steps, in order to make a multi-value printer give full scope to its unit performance by printing out an image using the multi-value printer even in response to binary image data, or in order to improve the quality of recovered character image:
Further, the image processing apparatus disclosed in the latter publication (referred to as a fourth conventional apparatus hereinafter) comprises the following means, in order to prevent the quality of image from deteriorating in the case of using a binarizing circuit having a simple structure using a dither method or the like, and also in order to constitute the image processing apparatus with simple circuits:
However, in the third conventional method, when setting a larger window, a shaded-off portion may be reproduced in the reproduced image. On the other hand, when setting a smaller window, a so-called Moire may be caused, resulting in deterioration of the reproductivity of the image.
Further, in the fourth conventional apparatus, since the image tone is judged by each block corresponding to the size of the dither matrix, the image tone can not be judged when the dither matrix of the binarizing circuit is not known, and also the image tone can not be judged when the image data to be judged are binarized using the other pseudo half-tone binarizing method. Furthermore, since the image tone is judged using the above-mentioned ROM, as the size of the dither matrix increases, the capacity of the ROM increases accompanying this, and then, it is necessary to provide a ROM having a relatively large capacity.
Furthermore, there is disclosed in the Japanese Patent laid-open publication No. 62-114377, an image processing method for converting binary image data of pseudo half-tone image into multi-value image data (referred to as a fifth conventional method hereinafter). In this publication, the following three methods are suggested.
Further, in the above-mentioned publication of the fifth conventional method, simultaneously when performing (3) the convolution process, an image emphasis process is performed using a Laplacian filter shown in FIG. 33.
Furthermore, there has been known to those skilled in the art, a conventional method for multi-value image data corresponding to the original image data based on a smoothed value and an edge emphasis value (referred to as a sixth conventional method hereinafter). Namely, a smoothing process is performed for binary image data within the window as described in the above-mentioned process (1) so as to calculate a smoothed value therefor. On the other hand, after calculating the edge emphasis amount within the window, multi-value image data corresponding to the original image data are recovered based on the calculated smoothed value and the edge emphasis value.
However, in the fifth conventional method, upon recovering multi-value image data having, for example, a natural number N or more of gradation stages, it is necessary to recover multi-value image data based on a natural number N or more of pixels. Further, when a recovery process is performed using a window having one side of length larger than an interval of the period of the original binary image data of pseudo half-tone image, a texture of the pseudo half-tone image may influence the recovered image. In order to solve the above-mentioned problems, it is necessary to use a relatively large window, and then, a circuit for counting the number of black pixels within the window becomes large-sized. Further, when there is an edge portion within the above-mentioned window, the edge portion is smoothed by the smoothing process of the fifth conventional method, so that the original image data may not be often recovered.
As described above, the edge emphasis amount used in the edge emphasis process and the edge judgment amount used upon judging whether or not there is an edge portion can be calculated based on an edge component amount or a relative amount of the edge component which is detected using the Laplacian filter shown in FIG. 33. However, when using the above-mentioned Laplacian filter, a high frequency component amount can not be accurately detected based on an image having a period of (7.times.2) dots, namely, the high frequency components of the edge portion are lowered. Further, since the direction of the edge component can not be detected, the edge component amount having taken the direction thereof into consideration can not be detected. In this case, an image which is not the edge portion may be erroneously detected as an edge portion, or any edge portion may not be detected within an image including an edge portion. Therefore, when recovering multi-value image data based on the edge component amount calculated by the above-mentioned Laplacian filter using the sixth conventional method, multi-value image data corresponding to the original image data can not be recovered.